In conventional multi-functional machine tools such as multi-functional milling machines, the multi-axial movement and rotation of the milling spindle and spindle head is controlled by remotely mounted motors which use timing belts, worm gears and worm wheels, bevel gears and parallel spur or bevel gears, individually or in combination, operably coupled to the spindle and spindle head to rotate the spindle and spindle head about multiple axes.
With the advent of linear motor technology and its application to machine tools, linear axes are being driven faster as cutting feedrates are being pushed higher. In the die and aerospace industries in particular, the machining of complex surfaces requires that the tool be kept at a particular angle with respect to the surface being machined. As the linear axis or contour of the surface being machined abruptly changes, a correcting movement is required by the rotary axis to maintain the required angular relationship between the tool and the surface being machined. For example, when a box shaped cavity is machined with a side wall-draft angle of 15 degrees, the tilt angle of the tool must be rotated 90 degrees at each quadrant point. To avoid slowing down the cutting process, the spindle head must be at 90 degrees at very high acceleration around the corner. This is difficult to achieve with a geared spindle head.
Thus, there remains a need for an operating spindle head which can be rotated at high speeds in response to the abrupt and continuous changes in the contour of a surface being machined so as to maintain the required angular relationship between the spindle head and such surface.